The actual odds of being hit by lightning

[Ixneigh]

So the idea of having a device to gradually bleed off charge to make your boat less attractive ie reduce the difference in charge between the cloud and the boat, is just bullock ?
I used to have a SS whip antenna on the mast top of my last several boats. Never got hit.
I redid the mast on my v22.2 and left off the antenna due to laziness. Got hit within a year. After that I installed a bolt that I sharpened the end off as a lightning rod.
I have heard that this will help form "streamers" of electrons that the lightening can then follow. (channels) but I always looked at it as reducing charge potential. You just don't want your boat to have the largest difference in charge of all the items available to hit, like buildings other boats and trees. Kind of like not being the slowest guy running away from a bear.
Ix

[Hamin' X]

The problem with the statistics about dissipators, is that they don't indicate whether the they were used in conjunction with a grounding system. Most people do not understand the principle and either ground the dissipators, or use a separate ground system. It is one, or the other. If you use dissipators, DO NOT GROUND; you will only be making yourself more attractive to lightning.

~Rich

[walt]

I have to admit that I am one who doesn’t understand why using a ground or not with a wire brush dissipater matters. As you mentioned, there are no statistics on this so there must be some theory or conclusion from something related? What is that evidence?

Recently there was a discussion on this web site regarding grounding or not grounding trying to see if there was any new stats.. http://forums.macgregor.sailboatowners. ... p?t=164729 Lots of technical stuff but still no actual data and a little bit of discussion on the wire dissipaters.

[walt]

an opinion..

On the cone of protection in an earlier post, the idea behind a lightning rod is that it is most likely to take the strike and therefore items within its protection won’t get struck. This also assumes that the lightning rod has a good way to dissipate the charge. On our sailboats, the mast is most likely to take the strike rather than the top of your head - so does offer some protection. But.. the bottom of the mast, shrouds, etc would be charged and likely to still flash to the water surface and that is why you want to stay away from them during lightning conditions. This was the idea behind the purple stripe I posted earlier. Pick a spot on the boat where you are likely the safest from metal to water discharge - such as from the bottom of the mast, side, front, back stays etc.

[walt]

Here is a little more discussion on the wire brush dissipaters.

Note that every paper or description or data on the wire brush dissipater have them electrically connected to ground – since the idea is that they are attempting to neutralize ground charge. As far as I can tell, the idea Rich has is that if you use one of these wire brush dissipaters, you don’t want it grounded. I have not seen this idea anywhere else – only from Rich and there are no statistics on this whatsoever on water which is why I was wondering what the theory is. I think there are a group of people here who can understand what the theory is, would find it interesting and would like to understand it.

A couple links on the wire brush dissipaters are here
http://www.lightningmaster.com/Resource ... ArtMID/559
http://alltecglobal.com/user-content/fi ... atalog.pdf

All of these papers note these work by enhancing Corona current which strips an electron from an air atom or molecule and the electron goes to the wire brush conductor and the left over positive ion floats upwards and away with the breeze. If that electron can make it to ground, it can nuetralize a single positive charge in the ground.

The first link shows some data taken by a university on grounded wire brush dissipaters of different configurations. Note that the typical electric field before a strike is about 5KV/meter and that experiment had the plates 3 meters apart so at the highest potentials in the graphs is 340 KV which would result in an electric field of 113 KV/Meter.

So even thought the peak electric fields in the graphs were over 20 times higher than normally seen before a lightning strike, the currents they were measuring at the very peak fields were still under 100 uA. The very highest current was like 300 uA.

This is a very tiny current. Compare this to the lowest current of any device on your boat – which maybe is a battery monitor and draws 5 to 10 ma. The leakage current of the battery monitor (which is very small) is on the order of 50 to 100 times LARGER than the current produced by the wire brush device. If you look at those graphs for actual fields of 5KV/meter which for the 3 meter distance would be 15KV, the currents are almost in the noise.

Now with the grounded wire brush device, it is putting that tiny charge into the water in an attempt to discharge the positive charge that has developed at the water surface. But water – even fresh water is conductive and electrically connected to the planet so the charge from the wire brush is infinitely small compared to the charge density in water and is quickly swept away.

And of course, these wire brush dissipaters are involved in boat lightning strikes. We of course have no idea if they are grounded or not or what the statistics are but the idea of them working is sort of like trying to empty the ocean with a tea spoon. Doesn’t make any sense.

Now consider the case with an ungrounded mast and a wire brush dissipater. You can find no information on this (except on this forum and we still don’t know the theory) but not grounding the mast will REDUCE the Corona current from the wire brush dissipater from the already tiny current of a grounded dissipater. The Corona current of the dissipater will actually charge the mast (not discharge it) but this will happen with or without the dissipater as even a slightly sharp point or edge on the mast will also create Corona current.

Now if you believe that a mast that is at some floating potential (which is what will occur) hides you from receiving a strike, that is your choice to believe. But I don’t know of any scientific evidence or statistical evidence to support this. A grounded wire brush dissipator will produce higher Corona current and I have seen some theory that higher Corona current creates a space charge that delays formation of a leader. So the only theory I know of says the wire brush dissipator would work better grounded and boats with them still get struck. But like a lot of stuff with lightning, this is just a theory, no evidence to support it.

DO NOT GROUND; you will only be making yourself more attractive to lightning.

I think you will also only find this advice on this forum. What is the idea here (besides that you need a ground to get your boat lights to work..).

[Hamin' X]

I find it interesting that lightning protection systems depend on grounded structures. If anyone wants to research the "rolling sphere" theory of protection, they will find that a grounded mast will attract lightning and prevent non grounded equipment from being struck, even though said equipment is closer to the last stepped leader from the cloud. Why would you want to make your mast more attractive to lightning than the surface of the water around you?

~Rich

[mastreb]

It's too bad Snopes can't just answer this one for us.

http://www.youtube.com/watch?feature=pl ... wr1a146gDg

[walt]

If anyone wants to research the "rolling sphere" theory of protection, they will find that a grounded mast will attract lightning and prevent non grounded equipment from being struck, even though said equipment is closer to the last stepped leader from the cloud

If I read this correctly, I think you just said that with the rolling shere method, a grounded mast will protect another ungrounded object that is within its sphere even though the ungrounded object is taller “ie, closer to the stepped leader”

Well… we might want to study the video in the link below. if you review the rolling sphere method, the protected objects will all be lower than the protection “mast”. Watch the video link below, the protected area is all in blue and everything protected is significantly lower than the protection mast. If what you meant to say is that a grounded mast will protect an ungrouned mast even though the ungrounded mast is taller but within the sphere – it doesnt work that way.. Please watch the video, note the blue protection area

https://www.youtube.com/watch?v=WGbQrcFlJDU

[Ixneigh]

re grounding...at its simplest is a cable hanging in the water. if its raining, the water film should be plenty conductive enough to supply the electrons for the streamer. i remember seeing a bolt hit the sea surface a few hundrex feet away. sparks jumped off the water. why was it more attractivethen my aluminum mast with a ss whip at the top?
Ix

[Hamin' X]

Walt, please don't try and tell me what I wrote, when it is there for anyone to read. You don't need to change my words. I did NOT say taller.

Ok, it has been many years since I have studied this stuff in depth, but you have made go and do your research. Here is a screen shot from a video on the subject.



Video link is complete with some of the math. It clearly shows that lightning will be attracted to the grounded structure, despite the fact that other structures are closer. It will also reveal that the lightning will be attracted to the closest grounded object. Refer to about 7 mins. in to the video. If a step leader is within strike distance of "ground", or "ground electrode". It means that even though you are within that sphere, IF YOU ARE NOT GROUNDED, YOUR HAVE NOTHING TO WORRY ABOUT.

https://www.youtube.com/watch?v=EtNxD08r0iY

~Rich

On Edit: I do not believe that any lightning protection, or avoidance scheme is 100% and that despite our best efforts, we can be struck.

~Rich

[walt]

If you use dissipators, DO NOT GROUND; you will only be making yourself more attractive to lightning.

Ok.. the video you posted (https://www.youtube.com/watch?v=EtNxD08r0iY ) is your proof for the above statement (did I get that right?), thanks for providing that.

[walt]

re grounding...at its simplest is a cable hanging in the water. if its raining, the water film should be plenty conductive enough to supply the electrons for the streamer. i remember seeing a bolt hit the sea surface a few hundrex feet away. sparks jumped off the water. why was it more attractivethen my aluminum mast with a ss whip at the top?
Ix

My opinion..

Your mast (grounded or not – I wasn’t able to make the same conclusion Rich did from watching that video a bunch of times as it had very little to do with a grounded or not grounded mast on the water and no statistics) forms an attractive node for lightning to strike but it will only pull in the leader somewhat defined by either its “cone of protection” or slightly more accurately, the area under the sphere shown in those video’s. If the lightning leader is far enough away, it would just go to the water surface. If the leader is close enough, the mast is a long conductor and creates an electric field short cut compared to air (grounded or not) and will attract the strike. The mast is the lowest impedance path compared to ionized air but the strike needs to be close enough in the first place.

The un-grounded boat has a “spark gap” between the mast and the water, the grounded boat is better at generating Corona current both of which are very slight detriments to a leader attaching to the mast. I don’t think anyone really knows the exact difference in the cone of protection each offers but the grounded boat would be better at surviving a strike. You could argue that the foam flotation that is in all of these boats is a form of lightning protection as the boat cant sink.

I don’t think you need rain involved. All that charge in the step leader creates a very high electric field and electric field ionizes air and also travels at the speed of light so has an influence ahead of the leader - ionized air is clearly is a good conductor -

[walt]

The rolling sphere videos were interesting and they show just how far a grounded mast will influence a leader - it’s on the order of a radius the lenght of the mast.. Outside of that range, the mast even with the best possible grounding won’t pull in the leader.

What exactly does "grounding" on the water mean? I consider it anything that will affect the electric fields. So a keel wrapped in glass would not be directly resistive to the water but from an electric field perspective, that insulated keel would be very close to ground potential so I would consider that grounded.

Our boats all have a mast that is insulated from the water surface by maybe 3 to 5 feet or so (except the X model which I think has a SS pole under the mast and our chain plates are actually a fair amount closer to the water surface) so we have a "spark gap" that is maybe 10 to 16% of the mast length. The X wouldl have a smaller "spark gap". How much does this influence pulling in a leader? I could give you my opinion again - very little, likely negligible - but my opinion isn’t any more valuable that anyone else’s here.

I have access to some high voltage generating equipment at work (for testing lightning vulnerability of consumer electronics) and recorded this video a while ago. What I did was make a small metal mast that was placed on a conductive ground plane (similar to a body of water) and run a high voltage discharge over the mast a few times and you can see how the mast will pull the discharge when it gets close to the mast.

I then created a spark gap under the mast so that it was completely insulated from the ground plane and duplicated running the high voltage source over the now "not grounded" mast.

You can see what difference the grounding made in the video. Nothing tricky about the video.. I wanted to see if there was any difference with the equipment I had available.

https://www.youtube.com/watch?v=X-siV6L ... e=youtu.be

It’s definitely not the same as lightning as the energy involved is a huge amount smaller but the electric field and air ionization principles are the same and it’s another data point to consider and also another piece of evidence why I dont think "grounding" has any significant influennce on your boat getting struck.

[Starscream]

If I follow the rolling sphere example, during a storm it sounds like I should sit up on the companionway hatch . The theory makes the X, with it's stainless pole through the cabin, sound relatively safe if one is just hanging out at the dinette or the settee. Maybe even chilling in the berths. Some dangerous conclusions might be made here.

Based on everything I have read on the internet (no misinformation there), I still have no idea what the right thing to do is so I am going to do....nothing. Just do my best not to get caught in a storm (re my decision to splurge on the Etec 90! ). If I do: everyone down below: no touching anything metal or electronic, and say your prayers.

[walt]

One other lightning/ boating accident I have heard of..

A while back, there was a discussion on a Hobie cat forum about lightning and at that time, I did a search for any lightning accidents with Hobie cats.. About the only thing I found was one guy was killed in a parking lot when lightning struck the mast he was taking down (mast was not grounded - still got struck). I don’t know the details but sounds like he may have been holding the mast when it got struck.

My opnion only but some pretty easy things to do with a boat like we have..

First, chances are really small of getting struck. But lightning is most likely to strike the mast and in our ungrounded boats, side flashes are likely to come out the bottom of the mast, on the stays, etc to the nearest water surface. So stay away from these metal parts during the storm.

Second, there was a kid killed a few years ago when they had beached a sailboat and he was in the water about waist deep going from the ladder to the shore. The sailboat may not have even been involved in the accident but apparently being in the water near the shore isn’t a good idea.

Spend as little time as possible around the mast if the conditions for lightning are present. This would of course include dropping the mast in the parking lot - even though once again the mast is not grounded..

Rolling sphere - a tool and method used to determine lightning protection for a facility. Doesn’t have much to do with our sailboats other than to point out that your mast is likely to get struck rather than you since you will be in the protected area under the mast - and that is a good thing. Just keep in mind that all that charge that entered the mast still has to get to the water and you don’t want to be involved in that current flow.